#include <bits/stdc++.h>
using namespace std;
using ll = long long int;
using ld = long double;
const int INF = 1 << 29;
const ll LINF = 1l << 61;
const ld PI = abs(acos(-1));
#define pq priotity_queue
#define mp make_pair
#define P pair
#define rep(i, a, b) for (ll i = (a); i < (b); i++)
#define rrep(i, a, b) for (ll i = (a); i >= (b); i--)
#define cbuf(buf, init) memset(buf, init, sizeof(buf))
#define modp(x, y) (((y) + (x) % (y)) % (y))
#define divd(x, y) (static_cast<double>(x) / static_cast<double>(y))

ll N, L[300000], K;

bool C(double l)
{
    ll s = 0;
    rep(i, 0, N){
        s += L[i] / l;
    }
    return s >= K;
}


int main()
{
    //
    cin >> N;
    rep(i, 0, N)    cin >> L[i];
    cin >> K;

    double lb = 0, ub = INF;
    rep(i, 0, 100){
        double mid = (lb + ub) / 2;
        if(C(mid))
            lb = mid;
        else
            ub = mid;
    }
    cout << fixed << setprecision(10)  << lb << endl;
}